Fatty acid cyclo-oxygenase present in human platelets is much more sensitive to aspirin than the enzyme present in human arterial tissue. This research proposal contains attempts to determine the nature of this increased sensitivity. The ability of intact human platelets to accumulate aspirin will be evaluated by a flow dialysis technique. Cyclo-oxygenase from platelets and vascular tissue will be isolated and their primary structures will be compared, primarily by peptide mapping techniques. The location of cyclo-oxygenase in subcellular fractions of human platelets will be determined and attempts will be made to obtain a subcellular fraction of human platelets containing cyclo-oxygenase and thromboxane synthetase activities. If successful this fraction will be used to evaluate the effect of drugs such as aspirin, synthetic prostaglandin analogues, and other compounds on platelet prostaglandin/thromboxane synthesis.